1. Explain it simply
然而 (rán'ér) means 'however' or 'yet'; it sounds more formal and written than 但是.
Word order: first clause + comma + 然而 + second clause, as in 大家都以为他会来，然而他没有来.
然而 heads the whole second clause - it does NOT sit after the subject the way 却 does.
It cannot fall to the end of the sentence or attach to the first clause before the comma.
2. Show examples
大家都以为他会来，然而他没有来。
Dàjiā dōu yǐwéi tā huì lái, rán'ér tā méiyǒu lái.
Everyone thought he would come; however, he didn't come.
然而 marks the unexpected turn
这件衣服很便宜，然而质量很好。
Zhè jiàn yīfu hěn piányi, rán'ér zhìliàng hěn hǎo.
This clothing is cheap; however, the quality is good.
然而 opens the second clause
天气看起来很好，然而突然下雨了。
Tiānqì kàn qǐlái hěn hǎo, rán'ér tūrán xiàyǔ le.
The weather looked nice; however, it suddenly rained.
a written-style contrast
3. Share a tip
然而 heads the clause, unlike 却 - say 然而他不喜欢, not 他然而不喜欢.